Yongliang Cheng

Formation mechanism of Fe2O3 hollow fibers by direct annealing of the electrospun composite fibers and their magnetic, electrochemical properties

Fe2O3 hollow fibers have been fabricated by direct annealing electrospun polyvinylpyrrolidone (PVP)/Fe(NO3)3 composite nanofibers. In this approach, composite fibers were firstly synthesized by electrospinning PVP/Fe(NO3)3 solution, and then calcined at high temperature with an appropriate heating rate to form hollow Fe2O3 fibers. The solvent composition, the addition amount of Fe(NO3)3·9H2O and PVP, and the heating rate have important influences on the morphologies of Fe2O3 fibers. Morphologies of Fe2O3 could be tuned from solid belt to hollow belts and hollow fibers by controlling appropriate preparation conditions. The crystal structure, morphology, surface composition, magnetic and electrochemical properties of the Fe2O3 hollow fibers were investigated by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, SQUID magnetometry and cyclic voltammetry, respectively.

Enhanced electrochemical properties of graphene-wrapped ZnMn2O4 nanorods for lithium-ion batteries

Thermally reduced graphene oxide (rGO)-wrapped ZnMn2O4 nanorods have been successfully fabricated via a facile bottom-up approach. Characterization results show that porous ZnMn2O4 nanorods are uniformly wrapped by ultrathin rGO sheets. The unique structure of this rGO–ZnMn2O4 composite could facilitate both ion and electron diffusion, thus providing suitable characteristics of an anode material for high performance lithium-ion batteries. Specifically, the conductive rGO sheets could act as an efficient buffer to relax the volume changes from Li+ insertion/extraction, and enable the structural and interfacial stabilization of ZnMn2O4 crystals. As a consequence, a high and stable reversible capacity (707 mA h g−1 at 100 mA g−1 over 50 cycles) and an excellent rate capability (440 mA h g−1 at 2000 mA g−1) are achieved with this composite material.

Magnetic and electrochemical properties of CuFe2O4 hollow fibers fabricated by simple electrospinning and direct annealing

Copper ferrite (CuFe2O4) hollow fibers were fabricated by direct annealing of electrospun precursor fibers with appropriate heating rate. The crystal structure, morphology, magnetic properties and electrochemical properties of as-made CuFe2O4 hollow fibers were investigated by using X-ray diffraction, Fourier-transformed infrared spectra, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometer, and electrochemical workstation. The results show that the appropriate heating rate of 0.5 °C min−1 can result in the formation of hollow tetragonal structural CuFe2O4 fibers. Hollow fibers after annealing at high temperatures still retain the one-dimensional texture and the walls of hollow fibers consist of many nanoparticles. Magnetization results indicate that the CuFe2O4 hollow fibers have a ferromagnetic behavior and their specific saturation magnetization value increases with an increase in the annealing temperature. Moreover, the electrochemical results suggest that the capacitance characteristic of the CuFe2O4 hollow fibers is a typical pseudocapacitive capacitance. The value of the specific capacitance gradually decreases with the increase in the discharge current density.

Preparation of TiO2 hollow nanofibers by electrospining combined with sol–gel process

TiO2 hollow nanofibers have been fabricated by directly annealing electrospun polyvinylpyrrolidone (PVP)/Tetra-butyl titanate (TBT) composite nanofibers. In this approach, PVP/TBT composite fibers were first synthesized by electrospinning PVP/TBT solution, and then calcined at high temperature with an appropriate heating rate to form hollow TiO2 nanofibers. During the heat treatment, the solvent composition, the amount of TBT and the heating rate have important influences on the morphologies of the TiO2 nanofibers. Morphologies of TiO2 could be tuned from solid nanofibers to belts, hollow nanofibers and rods by controlling the appropriate preparation conditions. The crystal structure, morphology, surface composition and specific surface area of the TiO2 hollow nanofibers were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller analysis, respectively.

Preparation of SrAl2O4:Eu2+, Dy3+ fibers by electrospinning combined with sol-gel process

One-dimensional SrAl(2)O(4):Eu(2+), Dy(3+) fibers were fabricated by a simple electrospinning combined with sol-gel process. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence were used to characterize the fibers. The results show that the phase structure of SrAl(2)O(4):Eu(2+), Dy(3+) belongs to a monoclinic one, the composite fibers and fibers calcined at high temperature remain the original one-dimensional texture, and the SrAl(2)O(4):Eu(2+), Dy(3+) was a green emission.

Fabrication of CoFe2O4 hollow fibers by direct annealing of the electrospun composite fibers and their magnetic properties

CoFe2O4 hollow fibers have been fabricated by direct annealing of electrospun polyvinylpyrrolidone (PVP)/nitrate salts composite nanofibers. In this approach, composite fibers were firstly synthesized by electrospinning PVP/nitrate salts solution, and then calcined at high temperature with appropriate heating rate to form hollow CoFe2O4 fibers. The crystal structure, morphology and magnetic properties of the CoFe2O4 hollow fibers were investigated by using the X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and SQUID magnetometry, respectively. The results indicate that the phase structure of hollow fibers belongs to cubic spinel structure, hollow fibers after annealing at high temperature still remain the one-dimensional texture and the wall of hollow fibers consists of many nanoparticles. The magnetic measurement showed that the hollow one dimensional structure has some novel magnetic properties, which may make them useful in electromagnetic and spintronic devices

Preparation of porous BiVO4 fibers by electrospinning and their photocatalytic performance under visible light

In this study, porous BiVO4 fibers were fabricated by a simple electrospinning technique followed by a controllable annealing of electrospun precursor fibers at different temperatures. The crystal structure, morphology, pore structure and photocatalytic properties of as-made porous BiVO4 fibers were systematically investigated. The results show that the final products have fibrous morphology and the phase structure of porous fibers belongs to monoclinic scheelite structure. The crystallinity and crystalline size increases, but the specific surface area decrease with increasing calcination temperature. These porous fibers all exhibit good optical absorption in visible light. As the sample calcined at 500 °C has larger specific surface area and better crystallinity, it exhibits the best photodegrading properties for rhodamine B solution.

Extension of imaging depth in two-photon fluorescence microscopy using a long-wavelength high-pulse-energy femtosecond laser source

We experimentally demonstrate, for the first time to the best of our knowledge, two‐photon fluorescence imaging with a femtosecond optical parametric amplifier. In particular, we systematically compare the imaging depths of two‐photon fluorescence microscopes based on three different excitation sources, including a femtosecond oscillator, a femtosecond regenerative amplifier and the optical parametric amplifier. The results show that the optical parametric amplifier can greatly extend the penetration depth by approximately 227% as compared with that obtained with the femtosecond oscillator due to effective suppression of scattering at longer wavelength and enhanced excitation efficiency enabled by higher pulse energy.

Morphology-controlled synthesis of gadolinium fluoride nanocrystalsvia ultrasonic and salt assisted method

Gadolinium fluoride NaxGdyFx+3y crystals with different morphologies and compositions have been successfully synthesized via a facile ultrasonic and salt assisted method at room temperature without any template or organic additive. Crystal structure and morphology of the fluorides were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Reaction conditions, such as ultrasonic irradiation, F/Gd molar ratio (R(F/Gd)), concentration of sodium nitrate and ultrasonic time have a close relationship with the morphology and phase composition of the final products. The growth mechanism of the uniform and monodisperse GdF3 nanospindles was proposed based on the time-dependent experiments. The photoluminescent (PL) properties of the as-obtained products revealed that Eu3+ doped NaGdF4 nanocrystals with different morphologies present characteristic luminescence of Eu3+, and their emission intensities strongly depend on morphology.

Effects of doping Y on crystal structure and catalytic activity of α-Bi2Mo3O12

Abstract The single phase Y0·2Bi1·8Mo3O12 and α-Bi2Mo3O12 catalysts have been synthesised by solid state reaction, and the Y0·2Bi1·8Mo3O12 shows better catalytic performance than α-Bi2Mo3O12 in the selective oxidation of isobutene to methacrolein. X-ray powder diffraction structural analysis, X-ray photoelectron spectroscopy and O2 temperature programmed desorption have been used to reveal the effects of doping Y on the crystal structure and catalytic activity of α-Bi2Mo3O12 induced by Y substitution for Bi. It is found that when Bi in α-Bi2Mo3O12 crystal structure is partially substituted by Y with lower electronegativity, the electronic densities of oxygen will increase, which could improve the rate determining α-H abstraction at Bi sites in the selective oxidation of isobutene to methacrolein. On the other hand, the partially regularised MoO4 tetrahedra also promote the catalytic selectivity to methacrolein due to the decrease in oxidation ability. Besides, the longer interatomic distances between Mo3 and Bi in the principal cleavage plane (010) and (010) might result in the lesser catalytic activity of Mo3 sites.